1. Field of the Invention
This invention generally relates to a method and an apparatus for detecting the positions of indices which differentiates an amount of transmission light or reflection light and are provided on an elongated base paper along its longitudinal direction with a predetermined distance therebetween (such as, labels or between labels) adhered to an elongated paper or eye marks printed on an elongated paper or notches formed on a tag paper.
2. Description of Prior Art
As to an apparatus of this kind, there is, for example, a label detection apparatus for a label printer as described in Japanese Patent Publication No. 1-44573.
This label detection apparatus detects the positions of the labels by comparing an output from a light detector with a predetermined standard value (a threshold value), wherein the light detector is installed on a feed path or an elongated base paper to which the labels are adhered so as to detect an amount of transmission light through both the portion of the base paper alone and the portion where the labels are adhered.
The apparatus detects and memorizes a peak value of an output from the light detector, and, based upon the memorized value, reestablishes a new standard value for a new label (every time the base paper is moved up for a distance of a pitch of the adhered labels).
Therefore, even if a detection level has changed due to changes of external lights or label paper quality, or by contamination on the light detector, the apparatus ensures the detection of label positions without fail by alternating the level of the standard value in response to those changes.
With the conventional apparatus, however, for each new upcoming label, a new standard value (a threshold value) is set, if an extraordinary detected value is put out in a range of a single-label detection (for example, in a case where the light detector passes over a hole or a perforation between labels), the extraordinary value is memorized as the peak value, and a new standard value is calculated and determined for the next label detection based upon the extraordinary value. Then, it becomes impossible to perform the subsequent label detection and the printer will cease to operate.
However, the above teachings of the conventional apparatus requires an operator even if there is nothing wrong in the printing of the labels.